The invention generally relates to projection systems, and more particularly, the invention relates to a projection system that includes a holographic beam splitter.
An ever-increasing number of applications are using display devices that are derived from a combination of liquid crystal optics technology and semiconductor technology. For example, these display devices may be used in mobile telephones, projection systems, home entertainment systems and monitors for personal computers.
One such display device is a spatial light modulator (SLM) that may be used in a projection system to form a modulated beam image. For color projection systems, the system may have one SLM for each primary color channel (red, green and blue (RGB) primary color channels, as examples) of the projection system. As an example, to form a projected multicolor image, one SLM may modulate a red beam (of the red channel) to form a red modulated beam image, one SLM may modulate a green beam (of the green channel) to form a green modulated beam image, and another SLM may modulate a blue beam (of the blue channel) to form a blue modulated beam image. In this manner, the red, green and blue modulated beam images combine on a projection screen to form the multicolor image.
Conventional projection systems may include optics to keep the beams of the different color channels separated. For example, referring to FIG. 1, a conventional reflective projection system 10 may include a light source 28 that generates a beam of white light. For purposes of separating the beam of white light into its primary red, green and blue beams (of the different color channels), the projection system 10 may include dichroic beam splitters 12 and 16. In this manner, the dichroic beam splitter 12 may separate a red beam, for example, from the white beam of light. A mirror 13 may reflect the red beam to a polarizing beam splitter 19 that, in turn, reflects the red beam to a reflective SLM 14 that modulates the red beam. The polarizing beam splitter 19 directs the resultant green modulated beam of light to an X-cube prism 24 that directs the modulated beam through projection optics 26 to form one component of the multicolor image, the green modulated beam image, on a projection screen (not shown). The projection system 10 typically includes additional optical devices, such as the dichroic beam splitter 16, and polarizing beam splitters 17 and 22 to direct the unmodulated green and blue beams (from the original white beam) to an SLM 18 and an SLM 20, respectively. The polarizing beam splitters 17 and 22 and the X-cube prism 24 direct the resultant green and blue modulated images through the projection optics 26 to form the remaining components of the multicolor image.
An example of a more compact conventional projection system 30 is depicted in FIG. 2. The projection system 30 uses a folded optics system that is formed from prism blocks 32, 34 and 36. In this manner, a light source 46 generates a white beam of light that is directed via a polarizing beam splitter 44 toward the prism blocks 32, 34 and 36. Dichroic optical coatings 35 and 41 may be used on some of the prism block faces to maintain the separation of the different color channels and to divide the white beam of light into the its primary red, green and blue beams. In this manner, the dichroic optical coatings 35 and 41 direct the red, green and blue beams of light to an SLM 38, SLM 40 and SLM 42, respectively. Once modulated, the modulated beams of light follow optical paths near (but in the reverse order) to the paths followed by the associated unmodulated incident beams of light to return to the polarizing beam splitter 44. The polarizing beam splitter 44, in turn, directs the modulated beams through projection optics 48 to form a multicolor image on a projection screen (not shown).
Unfortunately, the dichroic beam splitters may be quite expensive, and the filtering by the dichroic beam splitters may remove a large amount of light. Furthermore, the dichroic beam splitters are one of a number of optical devices that may make alignment of the modulated beam images cumbersome during calibration of the system 10, 30 and may introduce a significant amount of light loss due to the large number of reflective surfaces.
Thus, there is a continuing need for a system that addresses one or more of the problems stated above.
In one embodiment of the invention, a projection system includes at least one light source, at least one light modulator and a holographic beam splitter. The holographic beam splitter is adapted to establish optical communication between the light source(s) and the light modulator(s).
In another embodiment, a projection system includes at least one light source, at least one light modulator and a holographic beam splitter. The light source(s) are adapted to furnish unmodulated beams of light, and each unmodulated beam of light is associated with a different color channel. Each light modulator is associated with a different one of the unmodulated beams of light and is adapted to modulate the associated unmodulated beam of light to produce a modulated beam of light. The holographic beam splitter is adapted to direct each of the unmodulated beams of light to the associated light modulator.
In another embodiment, a method includes furnishing reference waves of light and recording interference patterns. Each reference wave of light is associated with a different color channel, and each of the interference patterns is associated with a different one of the reference waves of light. The interference patterns are used to produce object waves of light, and each of the object waves is associated with a different one of the color channels. The object waves are modulated to produce modulated light waves.
In yet another embodiment, a beam splitter includes a holographic medium that is adapted to receive beams of light that are associated with different color channels. The medium is adapted to direct the beams of light along optical paths that are situated at different angles based on the associated color channels.